ClustrMaps.com brings a widget that shows the location of your site visitors on a tiny map that could be easily put on your blog. They provide the HTML that gives you a tiny map. The location of each visit is based on the IP address of the computer used.

When it loads, it increments a counter and shows the locations of all visitors to your page. Clicking on it zooms in to a big world map, and (optionally) lets you zoom in to the continents, as in the example below